Flutter CircularProgressIndicator Freezes When Navigating to Another Page for a millisecond

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05-10-2024

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Flutter's Fading Flicker: Why CircularProgressIndicator Freezes on Navigation

Have you ever noticed a brief, jarring freeze in your Flutter app when navigating to a new page, accompanied by a lingering CircularProgressIndicator? This is a common issue that can be frustrating for users and detract from a smooth user experience. The culprit? A temporary pause in the app's UI thread while Flutter handles navigation.

Understanding the Problem

Here's a simplified scenario: Imagine you have a screen with a CircularProgressIndicator indicating ongoing data loading. When the user taps a button to navigate to another screen, Flutter begins the navigation process. This process involves:

1. Building the new screen: Flutter creates the widgets for the target screen.
2. Layout calculations: It determines the layout and positions of the new screen's widgets.
3. Rendering: Finally, the new screen is painted onto the device's display.

During this entire process, the UI thread is busy. This means that updates to the existing screen, including the CircularProgressIndicator, are temporarily halted. This brief pause can lead to the indicator freezing for a split second before the new screen appears, creating a noticeable flicker.

Example Code

Let's look at a typical code snippet where this might occur:

import 'package:flutter/material.dart';

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  bool isLoading = true;

  @override
  void initState() {
    super.initState();
    // Simulate data loading
    Future.delayed(Duration(seconds: 2)).then((_) {
      setState(() {
        isLoading = false;
      });
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('Loading Data')),
      body: Center(
        child: isLoading ? CircularProgressIndicator() : Text('Data loaded!'),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          Navigator.push(
            context,
            MaterialPageRoute(builder: (context) => AnotherScreen()),
          );
        },
        child: Icon(Icons.navigate_next),
      ),
    );
  }
}

class AnotherScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('Another Screen')),
      body: Center(
        child: Text('This is the new screen!'),
      ),
    );
  }
}

In this example, the CircularProgressIndicator will freeze briefly when the user taps the "navigate" button, resulting in the flickering effect.

Addressing the Issue

Here are some strategies to mitigate this flicker:

1. Utilize Navigator.pushReplacement: This approach replaces the current route with the new one, eliminating the need for a separate rendering step for the previous screen.

   Navigator.pushReplacement(
     context,
     MaterialPageRoute(builder: (context) => AnotherScreen()),
   );
   

2. Hide the CircularProgressIndicator: Before initiating the navigation, hide the progress indicator to prevent it from being displayed during the transition. You can achieve this by setting the isLoading state variable to false before calling Navigator.push.

   onPressed: () {
     setState(() {
       isLoading = false; 
     });
     Navigator.push(
       context,
       MaterialPageRoute(builder: (context) => AnotherScreen()),
     );
   },
   

3. Implement a smooth transition: Consider using a custom transition animation for smoother navigation, providing visual cues that indicate the ongoing process and minimizing the perceived delay. Flutter offers various transition options, like Fade, Slide, and Scale.

   Navigator.push(
     context,
     PageRouteBuilder(
       pageBuilder: (context, animation, secondaryAnimation) => AnotherScreen(),
       transitionsBuilder: (context, animation, secondaryAnimation, child) {
         return FadeTransition(opacity: animation, child: child);
       },
       transitionDuration: Duration(milliseconds: 500), // Adjust duration as needed
     ),
   );
   

4. Optimize your app performance: Minimize the amount of work done on the UI thread during navigation. Optimize your build methods for efficiency and avoid complex computations that can delay rendering.

Best Practices

• Keep the UI thread light: Avoid intensive tasks like network requests or complex calculations in the build method.
• Utilize futures and async/await: Use futures and async/await for asynchronous operations to offload work from the UI thread.
• Profile your application: Use Flutter's profiling tools to identify bottlenecks and improve performance.

By implementing these strategies and prioritizing efficient coding practices, you can create a seamless navigation experience for your users, eliminating the pesky flicker and enhancing overall app performance.